This invention relates to an optical distance measuring apparatus using the principle of triangulation.
A three-dimensional distance measurement is required in determing a three-dimensional shape or deformation, and such distance measurement has been widely conducted according to the principles of triangulation. As is well known, in the triangulation any one of the three sides constituting a triangle and the angles at both ends of the one side of the triangle are determined so that the triangle can be determined, and then the apex opposite to the one side in the so determined triangle is determined. FIG. 1 shows one example of measuring a distance from the nodal point of an observation lens to a given point on an object according to the principle of triangulation. As shown, two optical observation systems represented by observation lenses 1 and 2 are arranged a given distance "L" apart from each other with their optical axes parallel to each other. Then, the distance "Z" from the nodal point of the observation lenses 1 and 2 to a target "T" on an object 3 to be measured is given by: EQU Z=A.multidot.L/(Xa+Xb),
where "A" stands for a distance from the observation lenses 1 and 2 to an observation plane and "Xa" and "Xb" stand for distances from the optical axes of the observation systems 1 and 2 to those points on which the images of the target "T" appear on the observation plane.
A good accuracy with which a distance is determined according to the triangulation cannot be obtained without elongating the distance "L" between the two optical observation systems. As a result the whole apparatus is inevitably large in size. Therefore, the triangulation cannot be applied to such as an endoscope, which must be, in its nature, small in size.